Improved Aerodynamics of a Hollow-Blade Axial Flow Fan by Controlling the Leakage Flow Rate by Air Injection at the Rotating Shroud.

Michaël Pereira,Tarik Azzam,Hamid Oualli,Farid Bakir,Kamel Azzouz,Smaïne Kouidri,Florent Ravelet

doi:10.3390/e23070877

Abstract

Axial flow fans are used in many fields in order to ensure the mass and heat transfer from air, chiefly in the heating, ventilation and air conditioning industry (HVAC). A more proper understanding of the airflow behavior through the systems is necessary to manage and optimize the fan operation. Computational fluid dynamics (CFD) represents a real tool providing the ability to access flow structures in areas that measuring equipment cannot reach. Reducing the leakage flow rate, inherent in operation, by synthetic-jet techniques improves performance. This paper presents the CFD results performed on a hollow blade fan developed by our team. The leakage flow is controlled by blowing air from 16 designated circular holes and arranged on the fan shroud. We discuss the results for two rotational speeds (1000 and 2000 rpm) and two injection rates (400 and 800 L/min). The numerical results consistent with the experimental show, for the low rotation speed and high injection ratio, significant gains in power (53%), torque (80%) and leakage flow rate (80%).

Highlights

The leakage flow rate developed in the operating set has shown a great influence on the turbomachines
It was shown that the reduction in the dimension of the tip clearance leads to the reduction in both the size of the tip vortex and the amplitude of the noise
We investigate experimentally and numerically the effect of the active flow control by air injection in the tip clearance of axial flow cooling fan

Summary

Introduction

The leakage flow rate developed in the operating set has shown a great influence on the turbomachines This flow induced by the pressure difference either between the upper and lower surfaces of the blades, or between the upstream and downstream side of the device, is responsible for the energy losses and the generation of noise. Boudet et al [1] have numerically and experimentally investigated the leakage flow rate for an axial fan They showed that the major contribution of sound emission is induced by the tip vortex. With Delayed Detached Eddy Simulation (DDES) and the entropy analysis, Li et al [2] investigated the loss mechanism of the tip leakage flow. A reduction of around 11.6% was obtained for the total pressure drop coefficient

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